Evidence for the existence of two electronic states in the chalcopyrite-type alloys CuFe(S1−zSez)2

Results of Mössbauer spectroscopy for the chalcopyrite-type of alloys CuFe(S_1–z Se _z )₂ in the range of composition 0z0.45 are presented. Room temperature spectra show two contributions: one is a magnetic spectrum (six lines) with a value of the hyperfine field near to that of chalcopyrite (z=0, in which an antiferromagnetic order occurs belowT=823 K), the other having only one line. The relative area of the single-line contribution increases asz increases. Forz=0.2, we also made Mössbauer measurements as a function of temperature. The ratio of the two contributions evolves according to a Boltzmann law, in which the single line corresponds to the excited state at 81 K above the antiferromagnetic ground state.     

Electron localization in Fe2PO5

Fe₂PO₅ is a mixed valence compound where Fe^II and Fe^III are in face sharing octahedra with a short Fe^II - Fe^III distance, so that electron delocalization along chains parallel to the $\text{b}$ axis of the orthorhombic cell was worth to investigate. From Mössbauer experiments, carried out up to 600°C, it appears that the 4 lines spectra evolution, as regards Isomer Shift, Quadrupolar Splitting, and Linewidth, is only consistent with a localized electron pattern. This result is interpreted from the unequivalence of the 2 sites. The strong Fe^II quadrupolar splitting decrease allows the determination of the energy gap between the d_xy and d_yz-d_zx orbitals.     

Mossbauer effect measurements in the dysprosium-silicon and dysprosium-gallium equiatomic compounds

Mössbauer effect measurements have been performed in dysprosium-silicon and dysprosium-gallium equiatomic compounds. The experimental results were compared with crystal field calculations based on a point charge model. The calculated second order crystal field parameters were found to be predominant. The magnetic moment of the ground state is highly anisotropic and its high value (9.8 μ_B) is in good agreement with the observed magnetic hyperfine field which is similar for both the pure and the diluted compounds.The same magnitude of the quadrupolar interactions in these compounds as well as in the Dy metal may be attributed to the predominant contribution of the 4f electrons.     

Mössbauer study of f factors in iron carbonitrides

f-Factors of iron atoms, whith one and two interstitial nearest neghbours, in an iron carbonitride has been studied. Debye temperatures of 360 K and 620 K respectively, has been found.     

Electric field gradient sign determination in low magnetic fields perpendicular to the gamma rays in57Fe Mössbauer spectroscopy

The determination, by Mössbauer⁵⁷Fe spectroscopy, of the sign and the asymmetry parameter of the electric field gradient (EFG), in a non-magnetic powder sample, needs the use of an external magnetic field. Usually a “parallel-magnetic-field-to-the-gamma-rays” configuration is employed. In the present work, theoretically generated spectra in both configurations, parallel an perpendicular, are compared. The result is that the spectra in the perpendicular configuration show always a larger asymmetry for the same fields intensitics. In consequence, the sign determination of the EFG, is possible with magnetic fields significantly smaller in the perpendicular case than in the parallel one. Furthermore, the practical consequences are important, because EFG studies with conventional electromagnets, allowing only fields lower than 25 kGauss are feasible. As an example. Mössbauer experimental results obtained at room temperature for natural pyrite (FeS₂) in perpendicular fields of 15 and 20 kGauss, created by a conventional electromagnet, are shown here.     

Mössbauer study of hydrodemetallization clay catalysts of heavy oils: Role of pyrrhotites

The evolution of iron in clay catalysts employed in hydrodemetallization (HDM) of heavy oils has been studied by the Mossbauer effect. Pyrrhotites which appear during the process, were recognized as one of the active phases in HDM.Work partially supported by CDCH (Consejo de Desarrollo Científico y Humanistico de la Universidad Central de Venezuela).     

Electric field gradient produced by conduction electrons in rare earth metals

The electric field gradient produced by conduction electrons in the heavy rare earth metals has been calculated taking into account non-spherical effects due to the magnetic ordering in these metals. To our knowledge the values obtained are the first to agree with the sign of the experimental results.